unify track delegate handling

Summary:
In preparation for T6345 this diff unifies the delegates for the single album view and the all tracks view.
This makes adding i.e. new actions to both delegates a lot easier as they now share most of the code.
Two new track delegates are replacing the old ones. The delegate for the single album view only wraps around the shared code.
Included functional changes:
-animations in the single album view
-makes more data available in the models
-adds disc number handling for the all tracksview
-converted actions to use signals

Test Plan: album view and all tracks view work as before

Reviewers: Elisa, mgallien

Reviewed By: Elisa, mgallien

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D9261